1. Field of the Invention
The present invention relates to an electromagnetic valve that opens or closes a flow passage for fluid.
2. Description of Related Art
An electromagnetic valve disposed in a purge passage of an evaporated fuel treating device is conventionally known. For example, an electromagnetic valve described in JP-A-2006-308045 (corresponding to US2006/0243939A1) is formed by welding a covering member formed from resin to a peripheral edge part of an opening of a valve case formed from resin. The valve case is provided with an inlet port for introducing evaporated fuel, and an electromagnetic driving unit that is energized by the outside to reciprocate a valve member is attached to the valve case. The covering member is provided with an outlet port for discharging evaporated fuel, and a valve seat is formed on an end face of a cylindrical part of the covering member communicating with the outlet port. As a result of engagement of the valve member with the valve seat or disengagement of the valve member from the valve seat, the electromagnetic valve closes or opens a flow passage for evaporated fuel from the inlet port to the outlet port.
Generally, for example, poly butylene terephthalate (PBT) or polyamide (PA) 66 having resistance to fuel and flame resistance, is used as a resin material, from which the valve case and the covering member are formed. However, if alcohol fuel is contained in evaporated fuel, PBT or the like, which is easy to hydrolyze, is unsuitable. On the other hand, although not hydrolyzed, PA66 or the like can easily absorb water produced through alcohol dehydration reaction. If the covering member is formed from water-absorbing resin, because the peripheral edge part of the covering member is welded and fixed to the valve case, the covering member is deformed to crawl up outward in the valve axial direction when swollen due to the water absorption.
Particularly, if a chamber is provided inside the valve case on the inlet port-side as in the electromagnetic valve in JP-A-2006-308045, the valve axis is disposed to be eccentric relative to the central axis of the opening of the valve case. Accordingly, when the covering member crawls up to be deformed, deformation of the covering member on a longer-direction side from the valve axis is greater than deformation of the covering member on a shorter-direction side from the valve axis. As a result, the valve seat formed integrally with the covering member is inclined with respect to an end face of the valve member provided for the valve case, and a sealing failure may be caused at the time of engagement of the valve member with the valve seat.